With highly development and improvement of image-processing techniques, various electronic apparatuses including web camera, digital camera, cellular and picture phone, personal digital assistant (PDA), multimedia computer, etc., take advantages of these techniques to get well developed and enhanced. FIG. 1 shows a typical real-time image transmission architecture for implementing a digital image processing technique, wherein an image sensor 11, an image processor 12 with digital signal processing (DSP) function, and a memory buffer 13 are shown. The image sensor 11 picks up image of an object (now shown) under exposure and outputs the resulting image frame within a specified period of time for image-frame processing. Then the image processor 12 stores the image frame into the memory buffer 13 for subsequent processing. The image frame processed by the image processor 12 is optionally outputted to a computer or an image storage apparatus for further processing.
In the above-descried architecture, the image sensor 11 is generally implemented with a CMOS sensor or a CCD sensor, and the image processor 12 can be a digital signal processor (DSP). The image frame is generally presented in either RGB or YCbCr format depending on the choice of the image sensor 11. When the DSP 12 is to do a JPEG compression of the image frame, however, the image frame has to be in YCbCr format. Hence, it is necessary to use an image sensor capable of generating image data in YCbCr format to serve as the image sensor 11. Otherwise, if an RGB-type image sensor is used as the image sensor 11, additional RGB to YCbCr conversion has to be performed before the image data can be compressed by the image processor 12.
Conventionally, an image frame is stored in the memory buffer 13 and accessed by the image processor 12 as a whole. Therefore, the capacity of the memory buffer 13 should be large enough to accommodate the entire image frame. Moreover, under the requirement of receiving next image frame while processing currently stored image frame, the capacity of the memory buffer 13 should be enlarged to a level able to accommodate at least two image frames so as to prevent from improperly overwriting image data. Taking a VGA image frame consisting of 640×480 pixels for example, the storage capacity of the memory buffer 13 should be equal to or larger than (640×480 bytes)×3×2, which is about 1.8 MB. It is difficult to integrate such a large-sized memory buffer 13 with the image processor 12, and thus the memory buffer 13 generally stands alone. It is apparent that such arrangement is inefficient in manufacturing process and production cost.